Diatoms from the surface sediments of the South China Sea and their relationships to modern hydrography

A principal components analysis of diatoms in surface sediment samples from the South China Sea (SCS) shows a clear relationship between the spatial distributions of diatoms and the current pattern of the region. Six diatom assemblages are distinguished, representing environments with different hydrological characteristics. The neritic planktonic species Thalassionema nitzschioides is the dominant component in the surface sediment diatoms with relatively small changes throughout the SCS, suggesting that the water-mass exchanges between the SCS and the Pacific and Indian oceans are relatively small. The strongest impact of the warm, oceanic water occurs in the northeasternmost part of the SCS where Assemblage V is located with Nitzschia marina, Azpeitia nodulifera, Azpeitia neocrenulata, Rhizosolenia bergonii and Thalassionema frauenfeldii as main taxa. Warm, oceanic, planktonic species N. marina, R. bergonii and A. neocrenulata can be used as indicators of warm, oceanic waters flowing into the SCS in paleoceanographic reconstructions of the area, in particular in tracking the water from the western Pacific, including the Kuroshio Current. It may, however, be problematic to use another tropical, oceanic, planktonic species, A. nodulifera, as an environmental indicator because of its strong resistance to dissolution, thus possibly further transport.